aura: Implement app list M19 mock.

ash/shell/shell_main.cc

Index: ash/shell/shell_main.cc
diff --git a/ash/shell/shell_main.cc b/ash/shell/shell_main.cc
index 34611d3c93068ebc79adf4d35165cdabc8a0b037..19344b596cb8836c82d8ba56484527717c2003b2 100644
--- a/ash/shell/shell_main.cc
+++ b/ash/shell/shell_main.cc
@@ -178,10 +178,6 @@ class ShellDelegateImpl : public ash::ShellDelegate {
     MessageLoopForUI::current()->Quit();
   }
 
-  virtual void BuildAppListModel(ash::AppListModel* model) OVERRIDE {
-    ash::shell::BuildAppListModel(model);
-  }
-
   virtual ash::AppListViewDelegate* CreateAppListViewDelegate() OVERRIDE {
     return ash::shell::CreateAppListViewDelegate();
   }